In the fabrication of laminated safety glass, it is customary to place a piece of thermoplastic sheeting between two pieces of float glass. It is also common that the thermoplastic interlayer's surface can be roughened to avoid blocking, i.e., one layer of interlayer sticking to another. The roughness on the interlayer can also allow the interlayer to be moved while the two pieces of glass are aligned as the glass/interlayer/glass sandwich (hereinafter, “assembly”) is constructed. In constructing such an assembly, air is trapped in the interstitial space between the glass surface and the bulk of the thermoplastic interlayer. Trapped air can be removed either by vacuum de-airing or by nipping the assembly between a pair of rollers.
The degree to which air must be removed (reduced) from between the glass and interlayer will depend on the nature of the interlayer to absorb the air (dissolution) during further lamination steps, e.g., autoclaving, such that the air forms a ‘solution’ with the interlayer. The presence of a gaseous phase within the laminate will take the form of bubbles or pockets of gas between the interlayer and glass interface. These are generally objectionable for end-use applications where the laminate functions as a transparent article, which is, being essentially free of optical defects (e.g. relatively low-haze thus providing a transparent article without hindering visibility). Autoclaving is a step typically utilized in the production of laminated glass using a combination of heat and pressure to hasten the dissolution of any residual air (gaseous component) within the laminate assembly. As external pressure on the laminate is increased (by thermodynamic principals), it restricts the ability for gaseous components to either remain or to form. After the lamination process, the desire for creation of a ‘solid-phase’ interlayer, essentially free of a gas phase, is paramount. Additionally, the laminate should remain ‘bubble-free’ for a substantial period of time (years) under end-use conditions to fulfill its commercial role. It is not an uncommon defect in laminated glass for dissolved gasses to come out of solution (form bubbles or, delaminated areas between the glass/interlayer interface) as time progresses, especially at elevated temperatures experienced in automobiles, buildings and the like, often due to weather conditions and sunlight exposure.
In the case of vacuum de-airing, air is removed while the assembly is at ambient temperature. Tacking of the interlayer to the glass and sealing of the edges is accomplished by heating the entire assembly while it is still under vacuum. The assembly, after the heating step, is generally referred to as a pre-press or a pre-laminate.
In the case of nipping, the assembly is generally heated to a temperature between 50-100° C., and is then passed through one or more sets of nip rolls. Edge sealing is accomplished by the force of the rollers exerted on the two pieces of glass. At the end of the nipping step, the assembly is called a pre-press. In windshield manufacture, the nip rolls are often articulated so as to accommodate the curvature in the windshield. When complex shapes and angles are involved, or when several models of windshields are made concurrently, it is often more convenient to use the vacuum de-airing method.
However, laminators may encounter an issue when selecting a suitable interlayer. It is sometimes difficult to choose an interlayer with optimal features for pre-pressing, namely, rapid air removal and proper edge seal. Interlayers which have rougher surfaces as measured by the 10-point roughness (ISO R468), Rz, can allow for faster de-airing. However, such interlayers can make it inconvenient to obtain edge seal as more energy is generally required to compact the rough interlayer. If the edges of the pre-press are not completely sealed, air can penetrate the edge in the autoclaving step where the pre-press is heated under high pressure, and can cause visual defects in the laminate which is commercially unacceptable. Laminators who use vacuum for de-airing in hot environments can have added difficulty. Moreover, interlayers that are rough and allow for rapid de-airing at room temperature (23° C.) often do not de-air as well when the ambient temperature is much above 30° C.
On the other hand, relatively smooth interlayers can lead to edge sealing before sufficient air is removed, and can leave air trapped inside the pre-press. This problem is commonly referred to as pre-mature edge seal, and can be especially common with polyvinyl butyral (PVB) interlayers. During autoclaving, the excess air may be forced into solution under high pressure, but may return to the gas phase after autoclaving. Defects which occur after lamination are often more costly to rectify.
Safety glasses can be obtained using various types of interlayer materials, including, for example, PVB; thermoplastic polyurethane (TPU); ethylene copolymers such as ethylene vinyl acetate (EVA); silicone polymers; polyvinyl chloride (PVC); and ethylene acid copolymers and ionomers derived therefrom. Polymeric interlayer materials are thermoplastic. Thermoplastic interlayers are typically heated during the lamination process to soften the interlayer and facilitate adhesion to glass or plastic material. Surface patterns on the interlayers can be provided to allow for rapid de-airing even at high temperatures, and also allow good edge seal to be obtained. Choice or design of an ideal surface pattern can depend on the lamination process parameters as well as on the interlayer material. For example, plasticized PVB, which is often used in safety glass as an interlayer material, is tacky and can be readily adhered to glass even at room temperature. Various surface patterns can be used on the surface(s) of interlayer sheeting formed of plasticized PVB, but typically the patterns are designed to account for the physical characteristics of the specific interlayer and/or the specific process. For specific PVB interlayer surface patterns designed for safety glass glazing applications, see, e.g., U.S. Pat. Nos. 4,452,935; 5,091,258; 5,455,103; 5,626,809; 6,093,471; 6,800,355; and 6,863,956.
For interlayer sheeting formed from unplasticized high modulus polymeric materials, such as, ethylene acid copolymers or ionomers derived therefrom, the physical properties of such sheeting can be substantially different from those of the interlayer sheeting obtained from other materials, such as plasticized PVB. Due to these differences, surface patterns useful for plasticized PVB interlayer sheeting may not be ideal for interlayer sheeting that is formed of unplasticized high modulus polymeric materials, and vice versa. In accordance to the present invention, “high modulus polymeric materials” are those polymeric materials having a Storage Young's Modulus of 50-1,000 MPa (mega Pascals) at 0.3 Hz and 25° C. determined according to ASTM D 5026-95a. Polymeric materials that fall into this modulus range may include, but are not limited to, certain non-plasticized or low plasticized grades of polyvinyl butyral (PVB); polyurethane (PU); polyvinylchloride (PVC); metallocene-catalyzed linear low density polyethylenes; ethylenevinyl acetate (EVA); ethylene acid copolymers and ionomers derived therefrom; polymeric fatty acid polyamides; polyester resins such as poly(ethylene terephthalate); silicone elastomers; epoxy resins; elastomeric and crystalline polycarbonates; and the like.
Specifically, the surface patterns for interlayer sheeting formed of plasticized PVB, for example, tend to be deep to allow air to escape during the lamination process. The broad melting or softening range of plasticized PVB allows the use of such deep patterns. However, the use of deep patterns on interlayer sheeting formed of unplasticized high modulus polymers can be problematic. This is because sheets or films formed of unplasticized high modulus polymers are much stiffer than those formed of PVB, and therefore, during the pre-pressing process, more heat and/or energy will be required to compress such sheets or films having a deep surface pattern. In addition, sheets or films formed of unplasticized high modulus polymers, such as ionomers, in particular, are prone to attract dirt and therefore deep patterns tend to allow more dust or dirt to settle on the surface of the interlayer sheet or film and can give rise to “pattern haze” in laminates comprising the same. Also, the sharper melting range of an unplasticized, non-cured (non-cross-linked) interlayer sheet or film can lead to trapped air in the laminate.
The present invention provides certain surface patterns which can effectively facilitate de-airing during the lamination process when they are incorporated on the surface(s) of interlayer sheets or films formed of unplasticized high modulus polymeric compositions.